This invention relates to a process for the production of soluble instant coffee in powder form. More particularly, the invention relates to a process of this type in which coffee oil is obtained during the process and incorporated in coffee powder to obtain a product of enhanced flavour comparable with that of a coffee directly obtained by the percolation of boiling water through a bed of ground roasted coffee.
Soluble coffee powder is conventionally produced by freeze-drying or spray-drying after the evaporation of a coffee extract obtained by the percolation of an extraction liquid through cells filled with ground roasted coffee (Sivetz, Coffee Processing Technology, Vol. 1, pp. 262, 263, AVI, 1963).
When extraction is carried out in a countercurrent fashion, i.e., water under pressure at a temperature of 150.degree. to 180.degree. C. is introduced into a cell containing the batch of ground roasted coffee which has been most intensively extracted (having undergone N extractions) at the bottom of the cell. The liquid extract of this extraction cell is then passed through the extraction cell containing the batch of coffee which has been extracted (N-1) times and so on until the liquid extract passes through the cell which has just been filled with fresh ground roasted coffee.
Although the final extract obtained at the exit of the extraction cell containing the freshest coffee contains only a small quantity of ground coffee particles, fines still being entrained, it is desirable to filter the extract.
Finally, after the filtration phase which eliminates the particles larger than about 1 mm in size, solids, such as polysaccharides, are still present in suspension and are best eliminated to enable a coffee powder which dissolves perfectly without any solids appearing in the cup to be obtained after concentration and freeze-drying or spray-drying of the extract.
The suspended solids are normally eliminated by . centrifugation.
The final extract is then concentrated by evaporation and converted into powder form by freeze drying or spray drying.
One of the major problems of this type of process lies in the fact that the product obtained does not have the flavour of a roasted coffee which is due in particular to the evaporation and freeze-drying or spraying-drying steps which inevitably involve significant losses of aromas.
Various solutions have been proposed, comprising either spraying a coffee oil onto the coffee powder or incorporating a coffee oil in a jar filled with soluble coffee powder, for example by means of a syringe.
The coffee oil used may be enriched with coffee aromas, for example from recovery of the aromas of a ground roasted coffee. One process of this type is known, for example, from U.S. Pat. No. 3,406,074.
Hitherto, the coffee oil normally used has been obtained by pressing of a ground roasted coffee before extraction, one such process being described, for example, in British patent specification No. 1,532,662.
However, this method of recovering coffee oil by pressing, although effectively enabling a flavour-rich product to be obtained, is accompanied by a more or less pronounced smell of burning due to the temperature and pressure conditions required for pressing.
In addition, the highly volatile aromas tend nevertheless to escape. In addition, the oil obtained cannot be directly used on account of the large proportion of fine particles so that the oil has to be purified, for example by centrifugation.
Finally, this process involves the formation of a solid residue formed by the ground roasted coffee from which the oil was expressed.
In order not to eliminate this compact solid residue, which can be extracted, it has to be size-reduced so that it may be reintroduced into the coffee extraction columns, which inevitably involves a change in the taste of the end product that is more pronounced, the higher the ratio of recycled solid residue to the total quantity of roasted coffee extracted.
Accordingly, the process in question is complex in the equipment it requires, onerous because, if it is desired not to recycle the solid residue to avoid a change in quality, the cost of the pressed roasted coffee adds to the cost of the starting materials and, finally, is not entirely satisfactory in regard to the oil obtained which, although having a high resistance to oxidation in the crude state, shows distinctly less resistance to oxidation after deodorization with steam. Now, this operation is virtually compulsory due, on the one hand, to the smell of burning produced and, on the other hand, to the use of Robusta coffee to reduce the cost of the starting materials. Now, it is quite clear that it is not desirable directly to use an oil from the pressing of a roasted Robusta coffee for flavouring a coffee powder produced from an Arabica.
In order partly to overcome these disadvantages, it has been proposed to use the coffee grounds after extraction rather than pressing the ground roasted coffee before extraction. One such process is known, for example, from U.S. Pat. No. 3,035,921. However, even if this process avoids the use of non-extracted roasted coffee, the technique used is complex and, in addition, leads to an oil which, in the crude state, is not as stable as that directly produced from roasted coffee.
Accordingly, the problem addressed by the present invention was to enable a process for flavouring a coffee powder, such as that described in U.S. Pat. No. 3,406,074, to be used through the use of a coffee oil which, on the one hand, is even more stable than that produced by pressing of a non-roasted coffee and which, on the other hand, is easier to obtain and does not require the use of an additional source of starting materials.
It has been found that the final liquid extract issuing from the extraction cells contains a quantity of coffee oil of 0.2% to 0.5% by weight, based on the solid material present in the extract.
This oil source, although apparently very poor, has proved very interesting.
Thus, by means of a simple oil-extracting centrifuge arranged after the centrifuge which separates the suspended materials from the liquid extract after the filtration phase, it is possible to obtain approximately 90% of the total quantity of oil present in this extract.
In another embodiment, the two operations can be carried out in a single apparatus which separates the suspended materials, the oil and the liquid extract.
Now, this oil--ultimately readily obtainable--has the advantage of being far more stable than all known coffee oils and, in addition, is highly aromatic.
In sum the present invention provides a process wherein roast and ground coffee is extracted in a countercurrent fashion and then filtered to obtain an extract, coffee oil is separated from the extract and then the oil is incorporated into a soluble coffee powder.